1. Field of the Invention
The present disclosure relates to a magnetic resonance imaging (MRI) apparatus for diagnosing various diseases using MRI, and a manufacturing method thereof.
2. Description of the Related Art
In general, a medical imaging system is an apparatus that provides internal information about a patient as an image. Medical imaging systems include an X-ray machine, an ultrasonic diagnostic instrument, a computer tomography (CT) scanner, a magnetic resonance imaging (MRI) apparatus, etc.
The MRI apparatus holds an important position in the field of medical imaging diagnosis because image-taking conditions are relatively free and the MRI can provide excellent detectability and provide various diagnostic information images with respect to soft tissue.
The MRI causes nuclear magnetic resonance (NMR) in the hydrogen atomic nuclei of the human body using a magnetic field harmless to humans and RF which is non-ionizing radiation, to thus image the densities and physical or chemical characteristics of the atomic nuclei.
In more detail, the MRI apparatus supplies a specific frequency and energy to atomic nuclei in the state in which a constant magnetic field has been applied to the atomic nuclei, thereby causing the atomic nuclei to release energy, and converts the energy released from the atomic nuclei to signals, thereby diagnosing the inside human body.
When a magnetic field is applied to the atomic nuclei, protons configuring the atomic nuclei are arranged in the direction of the magnetic field since themselves have spin angular momentum and magnetic dipole moment, and the atomic nuclei perform precession with respect to the direction of the magnetic field. The precession causes nuclear magnetic resonance so that an internal image of the human body can be acquired through the nuclear magnetic resonance.
Meanwhile, the MRI apparatus applies a gradient field to a static field formed in a subject to thus acquire an image of the subject. Since a uniform static field should be formed in the subject, shims are provided for homogeneity of a static field formed by a static coil unit.
The shims may be provided inside the gradient coil unit forming gradient fields in a static field, or on the inner wall of the static coil unit.
Meanwhile, if passive shims are used, the passive shims are configured with tokens that can be comprised of iron and trays in which the iron tokens are accommodated. If current is applied to a gradient coil unit in order to form gradient fields in a static field formed in a subject, heat is generated by the resistance of the gradient coil unit.
The heat generation of the gradient coil unit may raise the temperature of the shim iron tokens, and if the temperature of the iron tokens is raised, homogeneity of the static field may deteriorate.
Accordingly, there is a need in the art for a technique capable of preventing the temperature of shim iron tokens from being raised such that the homogeneity of the static field deteriorates.